O’Neill gave “great credit” to Hearts for “going strongly at it and being able to stay there” and said Sunday’s clash between Celtic and Rangers can no longer be viewed as a title showdown.

Rangers are seven points adrift of the league leaders and four points behind defending champions Celtic, with second place still earning a shot at Champions League qualification.

“Rangers now are quite a number of points behind Hearts,” said O’Neill.

“We’re talking about three games left, so that would be difficult to overcome at this particular stage.

“It’s not impossible, it can happen. The games are very difficult matches still for all of us to come through.”

The Celtic manager added Hearts’ superior goal difference gives them the edge should their current advantage hold going into the final game of the season at Celtic Park.

“I suppose I was looking for a draw [between Hearts and Rangers]. A draw is very, very difficult to cheer on, but that would then have put it in our own hands,” the Northern Irishman said.

“As it turns out, mathematically speaking, it’s not actually in our own hands.

“But credit to the team, we’re still fighting, we still have a chance – there’s no question about it.”